Abstract

Biomineralisation is the process by which living things produce hard mineral
tissues with unique physical properties. The study of this process can help
us produce biomimetic materials, reproducing such properties, with the study of
nucleation and crystallisation of the materials being particularly important. I have
used molecular simulation techniques to help gain a greater understanding of these
processes, focussing particularly on identifying the conformations and solid phases
available to nanoparticles of two biomineral compounds.
The bones and teeth of mammals are made largely of calcium phosphates.
I have used metadynamics to study nanoparticles of tricalcium phosphate (TCP)
and have identified high and lower order configurations. To facilitate this work I
reviewed the extant empirical potentials for calcium phosphate systems, selecting
the most appropriate for TCP.
Calcium carbonate, found in examples throughout the animal kingdom, has
three crystalline polymorphs relevant to biomineralisation: calcite, aragonite and
vaterite. While nanoparticles of calcite have been extensively studied the other
polymorphs have been neglected to date. In this work I present a technique for predicting
crystalline morphologies for all three polymorphs across a range of sizes, and
compare the energetic ordering. In water the energetic ordering of the nanoparticles
is heavily dependent on nanoparticle size.
Furthermore, I present work calculating the surface enthalpies of a variety of
calcium carbonate surfaces, many of which are negative. It appears that entropic
penalty of ordered water is key to understanding the stability of nanocrystals.
Also presented is an application of the nudged elastic band method to study
transitions between nanoparticle crystal conformations. Between all three crystal
polymorphs the nanoparticles passed through an amorphous region of phase space.
These results have also been used to evaluate order parameters for use in metadynamics
simulations.